Based on the principle of overlapping internal validity among research designs, diagnose which study likely has higher internal validity and explain why.
Case context: A research team conducts a true experiment to test a new therapy for anxiety, randomly assigning participants to treatment or control groups. However, the therapy sessions are conducted by different therapists who vary widely in their empathy and experience, and the time of day for the sessions is not standardized. Another team conducts a quasi-experiment on the same therapy, comparing two intact clinic populations. They carefully match the clinics on socioeconomic status, use the exact same highly trained therapist for all sessions, and standardize the time of day and setting.
Question: Based on the principle of overlapping internal validity among research designs, diagnose which study likely has higher internal validity and explain why.
Sample answer: Although the first study is a true experiment (which generally sits higher on the design hierarchy), it is poorly designed and introduces significant confounding variables, such as therapist empathy and time of day. The second study is a quasi-experiment, but it is well-designed and carefully controls for potential confounds like setting, time, and therapist. Because of this overlap in execution quality, the well-designed quasi-experiment likely has higher internal validity than the poorly designed true experiment.
Key points:
- Identifies the quasi-experiment as having higher internal validity in this specific scenario.
- Explains that the true experiment introduces confounding variables (therapist differences, time of day).
- Recognizes that the quasi-experiment effectively controls for obvious confounds.
- Demonstrates understanding that actual study execution quality can override the general design hierarchy.
Rubric: The student should correctly identify that the quasi-experiment likely has higher internal validity and explain that the true experiment suffers from obvious confounding variables, demonstrating comprehension of how execution quality creates overlap in the design hierarchy.
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Research Methods in Psychology - 4th American Edition @ KPU
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